Speedup Cycles for material-only renders
To speed up Cycles, you are going to have to sacrifice realism.

If that is okay for your projects, you might try adjusting the filter glossy field, disabling Shadows, Caustics, and Bounce light, , like so:



Set the fields labeled, "Max" and "Min" to adjust the overall amount of Bounce Lighting, but note that this will also disable the "reflectiveness" of an object; If you don't want that, then adjust the fields bellow, with out changing the "Glossy" one.